In general, the copolymerization of monovinylarenes and dienes is conducted in a diluent. This copolymerization produces a mixture that comprises such diluent and a copolymer. After this copolymerization, steps are taken to remove as much of the diluent as possible from such mixture, in order to produce a composition that has a lower amount of diluent. It is desirable to have compositions with a lower amount of diluent because they can be more readily used in food and medical applications.
The prior-art-processes used to remove such diluent from such mixtures have not been satisfactory. The severe processing conditions to which such mixtures must be subjected, in order to achieve lower amounts of diluent in compositions made from such mixtures, have a profoundly detrimental effect on the quality of the final product. These severe processing conditions have the adverse effect of increasing the amount of imperfections in such compositions.
Copolymers of dienes and monovinylarenes contain main and side chain unsaturation (from the dienes) that make the copolymers especially prone to degradative changes in severe finishing operations. While this unsaturation makes finishing difficult it is primarily responsible for certain critically necessary properties that make these copolymers commercially important. The degradative changes in the copolymer due to severe processing can be quite varied and extensive. Included in these changes may be increased color, reduced copolymer stability, reduced stabilizer levels, and generally increased sensitivity to molding problems in a customer's plant. The most important of the degradative changes involves crosslinking and gelation of the copolymer to form gels (sometimes called "fisheyes") and black specks that show up as surface imperfections in product molding and especially in sheet and film applications. The more severe the finishing operation, the more extensive the degradative changes will be. A high level of gels and black specks are visually apparent in most commercial applications of these copolymers and are unacceptable to most customers.
Consequently, we have two competing priorities:
(1) a desire to produce compositions that comprise diluent and copolymer, where such compositions have a lower amount of diluent, and where such diluent comprises solvent and optionally volatiles, and where such solvent comprises aliphatic compounds, or alicyclic compounds, or mixtures of these compounds, and where such copolymer comprises polymerized monomers where said monomers are selected from the group consisting of monovinylarenes and dienes; and
(2) a desire to produce compositions that comprise diluent and copolymer, where such compositions have a lower amount of imperfections, and where such diluent comprises solvent and optionally volatiles, and where such solvent comprises aliphatic compounds, or alicyclic compounds, or mixtures of these compounds, and where such copolymer comprises polymerized monomers where said monomers are selected from the group consisting of monovinylarenes and dienes.
Until now, however, a process has not been developed that produces the desired compositions.
Therefore, the inventors provide this invention because the process of this invention will produce the desired composition, and consequently, this invention will be useful both economically and technologically to a producer of such compositions.